User interfaces for different kinds of electrical apparatuses are nowadays more and more often realized by means of different types of touch sensing devices based on touch sensitive films instead of conventional mechanical buttons. Here, mechanical buttons refers to related mechanical actuators such as on/off buttons, toggles, dials, rollers, sliders and switches. Different kinds of touch pads and touch screens of e.g. mobile phones, portable computers and similar devices are well known examples of these. In addition to the sophisticated and even luxurious user experience achievable, touch sensing devices based on touch sensitive films also provide a superior freedom to the designers continuously trying to find functionally more versatile, smaller, cheaper, lighter, and also visually more attractive devices.
A key element in such touch sensing devices is a touch sensitive film (TSF) comprising one or more conductive layers configured to serve as one or more sensing electrodes. The general operating principle of this kind of film is that the touch of a user by e.g. a fingertip or some particular pointer device changes the electrical properties of an electrical measuring circuitry to which the TSF is connected. The actual measuring principle can be e.g. resistive or capacitive, the latter one being nowadays usually considered the most advanced alternative providing the best performance in the most demanding applications.
One promising new approach for TSFs is found in layers formed of or comprising networked nanostructures. In addition to a suitable conductivity performance, a layer consisting of networks of e.g. carbon nanotubes (CNT), or carbon NANOBUD®s having fullerene or fullerene-like molecules covalently bonded to the side of a tubular carbon molecule (NANOBUD® is a registered trade mark of Canatu Oy), are clearly less visible to a human eye than e.g. transparent conductive oxides like ITO (Indium Tin Oxide). Besides, as is well known, nanostructure-based layers can possess flexibility, stretchability, thermoformability, mechanical strength and stability superior in comparison with e.g. ITO. These properties of nanostructure-based layers provide entirely new possibilities for designing touch-based user interfaces. For example, the flexibility or thermoformability of a TSF enables implementation of TSFs on three-dimensional surfaces. For example, in a mobile electronic device, the TSF can extend not only over the typically planar front surface but also to the sides of such a device. Such TSF can have several touch sensing regions. Then, the TSF can also be used, for example, to replace the mechanical buttons (i.e. related mechanical actuators such as on/off buttons, toggles, dials, rollers, sliders and switches) conventionally located on the sides of the device.
However there is still a strong demand in the market for further enhanced TSFs and touch sensing devices. Particularly, the transfer from conventional mechanical elements to user interfaces relying entirely on TSFs requires new solutions for improving the user experience.